The project was initiated to study the regulation of growth and differentiation of normal and chemically transformed cells using the rat hepatocarcinogenesis model in combination with quantitative two-dimensional electrophoresis. Results obtained to date include (1) using the Solt-Farber initiation promotion protocol, early preneoplastic hepatocytes were induced in male rats, isolated, and then separated into "small" and "large" cell populations using elutriation centrifugation. Following carcinogen treatment two major constitutive polypeptides (pI 5.7, MW 50 kDA and pI 6.6/49 kDa) were not detected in either "small" or "large" cells. In contrast, three new polypeptides (pI 6.5/53 kDA; pI 6.6/51 kDA; and pI 6.8/52 kDA) were expressed in both "small' and "large" cells put not in untreated control cells. "Small" and "large" cells showed no qualitative polypeptide differences. In contrast 8-10% of the 600-800 readily detected proteins were undergoing quantitative changes of at least four-fold during chemical carcinogenesis. (2) Individual hyperplastic liver nodules were dissected, and then classified histologically as being either early preneoplastic, preneoplastic, or neoplastic. Following carcinogen treatment one minor cytosolic polypeptide (pI 6.75/31 kDa) was not expressed in either preneoplastic or neoplastic nodules. However, four new cytosolic (pI 6.35/75 kDa; pI 6.8/57 kDa; pI 5.55/50 kDa; pI 6.1-5.7/57-60 kDa) and three membrane associated polypeptides (pI 6.25/48 kDa; pI 6.75/26 kDa; pI 6.05/24 kDa) were expressed in both neoplastic and preneoplastic nodules but not in normal liver. Numerous quantitative differences were also detected among the various cell types. (3) Investigations of the homogeneity/heterogeneity of gene expression among individual nodules isolated from separate animals have revealed marked similarities among the tissues analyzed.